SELECTIVE DRY ETCHING OF GaN OVER AlGaN IN BCL 3/ SF 6 MIXTURES

Inductively coupled plasma (ICP) etching of GaN with high selectivity over Al .22 Ga .78 N in BCl 3/ SF 6 mixtures has been studied. Selectivity and surface morphology were investigated over a wide range of pressures (3.75–37.5mTorr), RF powers (30–120 W), ICP powers (100–400 W), and SF 6/ BCl 3 ratios (0.1–0.7). Higher pressures, lower dc biases, and higher SF 6/ BCl 3 ratios increased the GaN to AlGaN selectivity. Selectivities up to 25 were measured by laser interferometry. A root mean square (rms) surface roughness of 0.67 nm was measured by atomic force microscopy (AFM) after removal of 0.5 μm from a GaN template (process selectivity: 15, as-grown rms surface roughness: 0.56 nm). A degradation in surface morphology, with the gradual formation of pits, was observed for selectivities above 10.